Update build system and packaging

Minimal changes required to integrate the SPL sources in to the
ZFS repository build infrastructure and packaging.

Build system and packaging:
  * Renamed SPL_* autoconf m4 macros to ZFS_*.
  * Removed redundant SPL_* autoconf m4 macros.
  * Updated the RPM spec files to remove SPL package dependency.
  * The zfs package obsoletes the spl package, and the zfs-kmod
    package obsoletes the spl-kmod package.
  * The zfs-kmod-devel* packages were updated to add compatibility
    symlinks under /usr/src/spl-x.y.z until all dependent packages
    can be updated.  They will be removed in a future release.
  * Updated copy-builtin script for in-kernel builds.
  * Updated DKMS package to include the spl.ko.
  * Updated stale AUTHORS file to include all contributors.
  * Updated stale COPYRIGHT and included the SPL as an exception.
  * Renamed README.markdown to README.md
  * Renamed OPENSOLARIS.LICENSE to LICENSE.
  * Renamed DISCLAIMER to NOTICE.

Required code changes:
  * Removed redundant HAVE_SPL macro.
  * Removed _BOOT from nvpairs since it doesn't apply for Linux.
  * Initial header cleanup (removal of empty headers, refactoring).
  * Remove SPL repository clone/build from zimport.sh.
  * Use of DEFINE_RATELIMIT_STATE and DEFINE_SPINLOCK removed due
    to build issues when forcing C99 compilation.
  * Replaced legacy ACCESS_ONCE with READ_ONCE.
  * Include needed headers for `current` and `EXPORT_SYMBOL`.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
TEST_ZIMPORT_SKIP="yes"
Closes #7556

module/icp/api/kcf_cipher.c

@@ -915,7 +915,7 @@ crypto_decrypt_single(crypto_context_t context, crypto_data_t *ciphertext,
 	return (error);
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 EXPORT_SYMBOL(crypto_cipher_init_prov);
 EXPORT_SYMBOL(crypto_cipher_init);
 EXPORT_SYMBOL(crypto_encrypt_prov);

module/icp/api/kcf_ctxops.c

@@ -145,7 +145,7 @@ crypto_destroy_ctx_template(crypto_ctx_template_t tmpl)
 	kmem_free(ctx_tmpl, sizeof (kcf_ctx_template_t));
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 EXPORT_SYMBOL(crypto_create_ctx_template);
 EXPORT_SYMBOL(crypto_destroy_ctx_template);
 #endif

module/icp/api/kcf_digest.c

@@ -482,7 +482,7 @@ crypto_digest_single(crypto_context_t context, crypto_data_t *data,
 	return (error);
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 EXPORT_SYMBOL(crypto_digest_prov);
 EXPORT_SYMBOL(crypto_digest);
 EXPORT_SYMBOL(crypto_digest_init_prov);

module/icp/api/kcf_mac.c

@@ -635,7 +635,7 @@ crypto_mac_single(crypto_context_t context, crypto_data_t *data,
 	return (error);
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 EXPORT_SYMBOL(crypto_mac_prov);
 EXPORT_SYMBOL(crypto_mac);
 EXPORT_SYMBOL(crypto_mac_verify_prov);

module/icp/api/kcf_miscapi.c

@@ -122,6 +122,6 @@ kcf_walk_ntfylist(uint32_t event, void *event_arg)
 	mutex_exit(&ntfy_list_lock);
 }
 
-#if defined(_KERNEL) && defined(HAVE_SPL)
+#if defined(_KERNEL)
 EXPORT_SYMBOL(crypto_mech2id);
 #endif